Tuner circuits used in present television receivers usually comprise an input stage being adapted for receiving two VHF bands and one UHF band and a downconverter with a mixer for downconverting respective analog and/or digital television channels. Usually an integrated IC solution is used comprising a three band mixer with a PLL controlled oscillator and an automatic gain controlled (AGC) IF amplifier. The integrated circuit downconverts a selected RF television channel to a standard intermediate frequency (IF). The downconverted signal is filtered by external filters being coupled to the integrated circuit, for example an IF bandpass filter and a SAW filter. The filtered signal is amplified by the AGC amplifier for providing an appropriate signal for a subsequent demodulator for demodulating the IF signal in accordance with a corresponding television standard.
An integrated tuner circuit of this kind is for example the IC CE5060 manufactured by the company Intel Corporation. A basic block diagram of this IC is shown in FIG. 1, which is shown in the data sheet for the CE5060 and available via internet, document no. D55748-001, February 2006. The CE5060 is a highly integrated circuit for multiband analog/digital terrestrial tuners and/or cable tuners and requires only little external circuitry for assembling a television tuner.
In the block diagram as shown in FIG. 1, the tuner comprises an RF input 1, which is coupled to low noise amplifiers and tunable tracking filters 2 for a first selection of a wanted television channel. The output signals of the low noise amplifiers and tracking filters 2 are coupled to a first amplifier stage 3 of the CE5060, which is followed by a mixer 4. The mixer 4 is controlled by a frequency synthesizer including a PLL controlled oscillator section 5 for downconverting a wanted television channel. The down converted signal is then passed to a second amplifier stage 6 followed by an IF filter 7 for providing a rejection of adjacent channels and an impedance transformation. The output signal of the IF filter 7 then passes to a SAW filter drive amplifier 8 for providing further amplification for a subsequent analog SAW filter 9 and a digital SAW filter 10. The IF filter 7 is for example a passive bandpass filter comprising capacitors and inductors, but no amplifying semiconductor elements.
The output signal of the analog SAW filter 9 is coupled to an analog demodulator 12 for demodulation of an analog television signal. The output of the digital SAW filter 10 is coupled to a gain-controlled IF amplifier 11 and then a digital demodulator 13 for demodulation of a digital television signal. The amplifier 11 is gain-controlled by the digital demodulator 13 via a control signal 15. The demodulators 12, 13 as well as the tuner circuit IC 1 are controlled via I2C bus 16.
New digital demodulators are in the meanwhile on the market, which incorporate also an analog NTSC demodulator, for example the single chip multistandard demodulator DRX 394yJ from the company MICRONAS and the AU8501 from the company Auvitek International. These demodulators are designed for application with a single tuner for DTV and analog NTSC reception and use a single differential IF input for both digital and analog IF signals.